diff options
Diffstat (limited to 'library/alloc/src/slice.rs')
| -rw-r--r-- | library/alloc/src/slice.rs | 97 |
1 files changed, 56 insertions, 41 deletions
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs index c7960b3fb49..9d704870326 100644 --- a/library/alloc/src/slice.rs +++ b/library/alloc/src/slice.rs @@ -78,7 +78,6 @@ pub use core::slice::{SplitInclusive, SplitInclusiveMut}; // N.B., see the `hack` module in this file for more details. #[cfg(test)] pub use hack::into_vec; - // HACK(japaric) needed for the implementation of `Vec::clone` during testing // N.B., see the `hack` module in this file for more details. #[cfg(test)] @@ -179,15 +178,25 @@ impl<T> [T] { /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) /// worst-case. /// - /// If `T: Ord` does not implement a total order the resulting order is unspecified. All - /// original elements will remain in the slice and any possible modifications via interior - /// mutability are observed in the input. Same is true if `T: Ord` panics. + /// If the implementation of [`Ord`] for `T` does not implement a [total order] the resulting + /// order of elements in the slice is unspecified. All original elements will remain in the + /// slice and any possible modifications via interior mutability are observed in the input. Same + /// is true if the implementation of [`Ord`] for `T` panics. /// /// When applicable, unstable sorting is preferred because it is generally faster than stable /// sorting and it doesn't allocate auxiliary memory. See /// [`sort_unstable`](slice::sort_unstable). The exception are partially sorted slices, which /// may be better served with `slice::sort`. /// + /// Sorting types that only implement [`PartialOrd`] such as [`f32`] and [`f64`] require + /// additional precautions. For example, `f32::NAN != f32::NAN`, which doesn't fulfill the + /// reflexivity requirement of [`Ord`]. By using an alternative comparison function with + /// `slice::sort_by` such as [`f32::total_cmp`] or [`f64::total_cmp`] that defines a [total + /// order] users can sort slices containing floating-point values. Alternatively, if all values + /// in the slice are guaranteed to be in a subset for which [`PartialOrd::partial_cmp`] forms a + /// [total order], it's possible to sort the slice with `sort_by(|a, b| + /// a.partial_cmp(b).unwrap())`. + /// /// # Current implementation /// /// The current implementation is based on [driftsort] by Orson Peters and Lukas Bergdoll, which @@ -199,18 +208,21 @@ impl<T> [T] { /// handled without allocation, medium sized slices allocate `self.len()` and beyond that it /// clamps at `self.len() / 2`. /// - /// If `T: Ord` does not implement a total order, the implementation may panic. + /// # Panics + /// + /// May panic if the implementation of [`Ord`] for `T` does not implement a [total order]. /// /// # Examples /// /// ``` - /// let mut v = [-5, 4, 1, -3, 2]; + /// let mut v = [4, -5, 1, -3, 2]; /// /// v.sort(); - /// assert!(v == [-5, -3, 1, 2, 4]); + /// assert_eq!(v, [-5, -3, 1, 2, 4]); /// ``` /// /// [driftsort]: https://github.com/Voultapher/driftsort + /// [total order]: https://en.wikipedia.org/wiki/Total_order #[cfg(not(no_global_oom_handling))] #[rustc_allow_incoherent_impl] #[stable(feature = "rust1", since = "1.0.0")] @@ -222,30 +234,19 @@ impl<T> [T] { stable_sort(self, T::lt); } - /// Sorts the slice with a comparator function, preserving initial order of equal elements. + /// Sorts the slice with a comparison function, preserving initial order of equal elements. /// /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) /// worst-case. /// - /// The comparator function should define a total ordering for the elements in the slice. If the - /// ordering is not total, the order of the elements is unspecified. + /// If the comparison function `compare` does not implement a [total order] the resulting order + /// of elements in the slice is unspecified. All original elements will remain in the slice and + /// any possible modifications via interior mutability are observed in the input. Same is true + /// if `compare` panics. /// - /// If the comparator function does not implement a total order the resulting order is - /// unspecified. All original elements will remain in the slice and any possible modifications - /// via interior mutability are observed in the input. Same is true if the comparator function - /// panics. A total order (for all `a`, `b` and `c`): - /// - /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and - /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. - /// - /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use - /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`. - /// - /// ``` - /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0]; - /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap()); - /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]); - /// ``` + /// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor + /// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and + /// examples see the [`Ord`] documentation. /// /// # Current implementation /// @@ -258,21 +259,24 @@ impl<T> [T] { /// handled without allocation, medium sized slices allocate `self.len()` and beyond that it /// clamps at `self.len() / 2`. /// - /// If `T: Ord` does not implement a total order, the implementation may panic. + /// # Panics + /// + /// May panic if `compare` does not implement a [total order]. /// /// # Examples /// /// ``` - /// let mut v = [5, 4, 1, 3, 2]; + /// let mut v = [4, -5, 1, -3, 2]; /// v.sort_by(|a, b| a.cmp(b)); - /// assert!(v == [1, 2, 3, 4, 5]); + /// assert_eq!(v, [-5, -3, 1, 2, 4]); /// /// // reverse sorting /// v.sort_by(|a, b| b.cmp(a)); - /// assert!(v == [5, 4, 3, 2, 1]); + /// assert_eq!(v, [4, 2, 1, -3, -5]); /// ``` /// /// [driftsort]: https://github.com/Voultapher/driftsort + /// [total order]: https://en.wikipedia.org/wiki/Total_order #[cfg(not(no_global_oom_handling))] #[rustc_allow_incoherent_impl] #[stable(feature = "rust1", since = "1.0.0")] @@ -289,9 +293,10 @@ impl<T> [T] { /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*)) /// worst-case, where the key function is *O*(*m*). /// - /// If `K: Ord` does not implement a total order the resulting order is unspecified. - /// All original elements will remain in the slice and any possible modifications via interior - /// mutability are observed in the input. Same is true if `K: Ord` panics. + /// If the implementation of [`Ord`] for `K` does not implement a [total order] the resulting + /// order of elements in the slice is unspecified. All original elements will remain in the + /// slice and any possible modifications via interior mutability are observed in the input. Same + /// is true if the implementation of [`Ord`] for `K` panics. /// /// # Current implementation /// @@ -304,18 +309,21 @@ impl<T> [T] { /// handled without allocation, medium sized slices allocate `self.len()` and beyond that it /// clamps at `self.len() / 2`. /// - /// If `K: Ord` does not implement a total order, the implementation may panic. + /// # Panics + /// + /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order]. /// /// # Examples /// /// ``` - /// let mut v = [-5i32, 4, 1, -3, 2]; + /// let mut v = [4i32, -5, 1, -3, 2]; /// /// v.sort_by_key(|k| k.abs()); - /// assert!(v == [1, 2, -3, 4, -5]); + /// assert_eq!(v, [1, 2, -3, 4, -5]); /// ``` /// /// [driftsort]: https://github.com/Voultapher/driftsort + /// [total order]: https://en.wikipedia.org/wiki/Total_order #[cfg(not(no_global_oom_handling))] #[rustc_allow_incoherent_impl] #[stable(feature = "slice_sort_by_key", since = "1.7.0")] @@ -337,9 +345,10 @@ impl<T> [T] { /// storage to remember the results of key evaluation. The order of calls to the key function is /// unspecified and may change in future versions of the standard library. /// - /// If `K: Ord` does not implement a total order the resulting order is unspecified. - /// All original elements will remain in the slice and any possible modifications via interior - /// mutability are observed in the input. Same is true if `K: Ord` panics. + /// If the implementation of [`Ord`] for `K` does not implement a [total order] the resulting + /// order of elements in the slice is unspecified. All original elements will remain in the + /// slice and any possible modifications via interior mutability are observed in the input. Same + /// is true if the implementation of [`Ord`] for `K` panics. /// /// For simple key functions (e.g., functions that are property accesses or basic operations), /// [`sort_by_key`](slice::sort_by_key) is likely to be faster. @@ -356,16 +365,22 @@ impl<T> [T] { /// In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the /// length of the slice. /// + /// # Panics + /// + /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order]. + /// /// # Examples /// /// ``` - /// let mut v = [-5i32, 4, 32, -3, 2]; + /// let mut v = [4i32, -5, 1, -3, 2, 10]; /// + /// // Strings are sorted by lexicographical order. /// v.sort_by_cached_key(|k| k.to_string()); - /// assert!(v == [-3, -5, 2, 32, 4]); + /// assert_eq!(v, [-3, -5, 1, 10, 2, 4]); /// ``` /// /// [ipnsort]: https://github.com/Voultapher/sort-research-rs/tree/main/ipnsort + /// [total order]: https://en.wikipedia.org/wiki/Total_order #[cfg(not(no_global_oom_handling))] #[rustc_allow_incoherent_impl] #[stable(feature = "slice_sort_by_cached_key", since = "1.34.0")] |